东海盆地西湖凹陷凝析气藏成藏特征及分布控制因素

实际勘探证实西湖凹陷油气藏具有上油下气的特征，油气资源分布表现为南多北少。通过西湖凹陷凝析油和凝析气地球化学参数的分析，认为西湖凹陷的凝析油和凝析气具有相同的成因类型和成熟度，均为平湖组煤系源岩生成的油气。根据西部斜坡带和中央反转带油气藏类型、油气成藏期次及圈闭形成时间研究成果，认为：西部斜坡带油气首先充注在平湖组中，后期由于断层开启调整至花港组中，因压力降低油气分离和天然气散失而在花港组中形成凝析油藏；在中央反转带，由于圈闭定型时间晚，油气主要经历一期成藏再通过断层运移至花港组，花港组上部压力低，使油气分离、天然气散失而形成纯凝析油藏。通过对油气成藏和分布特征的研究，认为生烃中心的分布控制着油气藏的分布，断层分布和断穿层位控制着油气藏丰度，超压控制着西部斜坡带凝析油和凝析气藏的分布界面。

Characteristics and Controlling Factors of Condensate Reservoir Accumulation in Xihu Sag,East China Sea Basin

Based on a plenty of exploration achievements in Xihu sag, it is found that the oil reservoir is distributed in the upper stratum, while the gas is distributed in the lower stratum, with the pattern of more resources in the southern fields than those in northern ones. Through the analysis of the geochemical parameters of the condensate and condensate gas in Xihu sag, it is concluded that the condensate and condensate gas are the same for their genetic type and maturity, and are generated from the coal measures source rocks of Pinghu Formation. Based on the research results of reservoir type, oil and gas accumulation time,and trap forming time in the western slope and central inversion belts, it is believed that the oil and gas filled in Pinghu Formation in the western slope belt, and then migrated to Huagang Formation due to the late fault opening. Because the pressure was reduced in Huagang Formation, gas was lost, and finally the condensate reservoir was formed in Huagang Formation. In the central inversion zone, due to the late trap, oil and gas underwent one time reservoir accumulation, and then migrated to Huagang Formation through faults. Because the low pressure in the upper part of Huagang Formation, oil and gas were separated with gas dispersing, thus the pure condensate reservoir was formed. According to the research on the attributes of oil/gas accumulation and distribution, we can get the conclusion as follows:the reservoir distribution is controlled by the gas-generation center, and the abundance is controlled by faults; the distributing interface between condensate oil reservoir and condensate gas reservoir is controlled by overpressure in the west slope belt.